FMEA Action Priority Calculator (S, O, D)
Enter severity, occurrence and detection. The calculator returns a High, Medium or Low action priority using severity-first precedence, shows the exact rule that produced it, and demonstrates why ranking by RPN misleads.
Runs entirely in your browser. Nothing is uploaded, stored, or sent anywhere.
Why RPN was retired
For decades FMEA teams ranked risk by the risk priority number: severity times occurrence times detection. It is an appealing idea and a bad one, because multiplication throws away exactly the information that matters. A severity of 10 with an occurrence of 2 and a detection of 5 gives 100. So does a severity of 5, an occurrence of 4 and a detection of 5. The first is a potential safety or regulatory failure; the second is an annoyance. Treated as equal, they get the same attention, and the queue gets worked from the top of a list that is sorted by the wrong thing.
The replacement is a precedence rule rather than a product. Severity is considered first, because a severe effect deserves attention even when the cause is rare. Occurrence is considered second. Detection is considered last, because detection is the weakest of the three: catching a problem later is worth much less than not causing it, and detection ratings are the most optimistically scored of the three in practice.
The output is not a number to sort by. It is a High, Medium or Low action priority, and each carries an obligation. High means the team acts or documents why not. Medium means it should act or record why the current controls suffice. Low means it may act, and should still record the rationale. Nothing is ever silently dropped.
Reading the three scales honestly
- Severity is a property of the effect, not the cause. It does not move because a cause is unlikely. If a failure can injure someone, the severity stays high however rare it is — that is the whole reason the rating exists.
- Occurrence is about the cause, not the failure mode. Rating it against the mode instead of the specific cause is the most common scoring error, and it usually inflates the number.
- Detection means detection before the customer. Not detection during warranty analysis. A control that finds the problem after shipment is not detection, and rating it as such quietly hides real risk.
- Detection can never rescue a severe failure. Improving detection on a safety-related item does not reduce its severity, and a design that depends on inspection to be safe has not been made safe.
Where this fits
FMEA and FMEDA review is one of our primary service lines. The most common finding in a review is not arithmetic at all — it is that severity has been argued down to make a number look better, or that actions were recorded with no verification that they closed the risk. A review runs one to two weeks and ends in a written report you keep. For the hardware side of the same question, the FMEDA rollup calculator shows where your quantitative metrics are being spent.
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